Love is what one creates. It's the only way we know how to describe the sensation of attraction, and the feeling is much different than just being "happy".
When someone says that they love you, it's because you make them feel like that. Better than the best thing in the world, I guess.
What do I know, though
EDIT - After re-reading this post, I realize that it reeks of a 7th grade Honor's English class. Forgive me.